Queensland is in the grip of another extraordinary flood crisis, as cities and towns across the state go under.

At least three people are dead and residents in the state's capital are being warned to brace for the worst as 3600 residential properties and 1250 businesses are expected to experience flooding when the Brisbane river peaks on Tuesday.

VIDEO: A car stuns police and onlookers on the Sunshine Coast, almost running down two police officers after driving while completely submerged by a blanket of froth.

A three-year-old boy is in a critical condition in hospital after a tree fell on him and his mother on Brisbane’s northside.

They were on the banks of Kedron Brook at Gordon Park when the large tree ripped loose from the sodden ground and suddenly fell, trapping them. The boy’s 30-year-old mother is also being treated in hospital for head injuries.

Meanwhile, dramatic rescues were conducted in Bundaberg on Monday afternoon after that city's worst flood on record left dozens of people trapped on rooftops.

About 200 properties have already been flooded in the city. On Monday afternoon, Premier Campbell Newman warned water was flowing so fast into North Bundaberg it could rip houses from their foundations and sweep them down the river.

About 1500 people were trapped after staying in their houses despite a mandatory evacuation order issued to the 5000 people in the area.

"Look, the issue we've got right now in Bundaberg is we are at a point where we've never seen floodwaters like this before," Mr Newman said.

"People...probably feel, quite reasonably, that they've seen this all before and they feel they can be safe in certain parts of North Bundaberg.

"Right now our view is they are not, and that's why we need to get them out.

"Again I stress, we will do anything we can to get them out."

Fourteen helicopters have been used to rescue people from the stricken city.

The situation is so bad that police are advising people trapped in homes in North Bundaberg to seek refuge on the roof.

"If your house is currently inundated with water and you require rescuing, you are either to make your way to the roof if safe - I repeat - if safe," Senior Sergeant Grant Marcus said in an urgent public alert issued on Monday morning.

"Alternatively find a way by which you can hail rescue helicopters which are currently hovering over your area."

The communities of Gympie and Maryborough are also under water. There is also a major flood crisis gripping the Lockyer Valley, where 19 lives were lost in the state's 2011 floods.

VIDEO: Flooding in Brisbane's central business district.

So far, three flood deaths have been confirmed: an 81-year-old man whose body was pulled from the water near Bundaberg, a 27-year-old wheelchair-bound man who was found near Gympie, and a third person, believed to be a male motorcyclist, who was swept off the road at Greenbank, near Ipswich. Police confirmed a body had been found in Oxley Creek about 7am.

Prime Minister Julia Gillard has offered her condolences to the families of the three victims, saying the floods had ''broken a lot of hearts''.

Ms Gillard, touring bushfire-affected parts of Victoria, said nature was challenging the nation but people would ''get through this'' by pulling together.

The comments came as Opposition Leader Tony Abbott visited an SES depot in Brisbane to fill sandbags.

Deputy Prime Minister Wayne Swan, meanwhile, has visited Goodna, west of Brisbane, where residents have also been put on flood alert.

Ms Gillard believed the current events would present a particularly difficult time psychologically for residents in the Lockyer Valley.

''Given everything that has happened in Queensland over the last two years this is a particularly heart-breaking time for people,'' Ms Gillard said.

''Whether it’s bushfires, whether it’s floods we are being challenged by nature, but we are a strong and smart nation and we will get through this like we always do, by pulling together,'' she said.

Ms Gillard said she had spoken to Queensland Premier Campbell Newman and offered to assist.

So far, the Australian Defence Force has provided Black Hawks to help flood-affected communities.

Insurance claims from the latest Queensland floods have already topped $43 million, as river levels continue to rise in large parts of the state.

As early as Monday afternoon, about 5050 claims had been lodged relating to losses from the major rain event now affecting Queensland and New South Wales, said Campbell Fuller, general manager for communications at the the Insurance Council of Australia.

The total claimed losses are likely to be reach $50 million by mid week, he said.

"Rivers are still rising across south-eastern Queensland," he said, adding that flood waters were yet to peak at Ipswich and much of Bundaberg remained underwater.